The increasing demand for digital video/audio information presents an ever increasing problem of monitoring the transmission or storage of data in data communication. As the transmission bandwidth increases in response to greater demand, it becomes increasingly more difficult to monitor the enormous amount of transmitted information in real time.
Generally, the data streams contain video, audio, timing and control data which are packaged into various “packets”. A packet is a group of binary digits that include data and control elements which are switched and transmitted as a composite whole. The data, control elements and other information are arranged in various specific formats.
Examples of such formats are disclosed in the ISO/IEC international Standards 11172 (1994) (generally referred to as MPEG-1) and 13818 (Jan. 20, 1995 draft) (generally referred to as MPEG-2), which are incorporated herein in their entirety by reference. In general, MPEG defines a packet as consisting of a header followed by a number of contiguous bytes from an “elementary data stream”. An elementary stream is simply a generic term for one of the coded video, coded audio or other coded bitstreams. More specifically, a MPEG-2 “transport stream” packet comprises a header, which may be four (4) or more bytes long with a payload having a maximum length of 184 bytes. Transport stream packets are part of one or more programs which are assembled into a transport stream. The transport stream is then transmitted over a channel with a particular transfer rate.
Thus, in order to monitor and evaluate the status of a transport stream in real time, a method or apparatus must be able to handle the high transfer rate of the transmission channel. To illustrate, if data from the transport stream is arriving at a rate of 5 Mega-bytes per second and a processing unit operates at 20 Mega-instructions per second, then the processing unit must perform, on average, a READ operation every fourth instruction. This requirement is computationally expensive and increases the cost of performing real time packet analysis. In fact, since time is such a scarce resource in real time packet analysis, it may become prohibitively expensive. Although it may be more cost effective to capture the data in the transport stream into storage and then analyze the data at a later time, the benefit of real time analysis is lost. These benefits may include the detection of packet framing errors, jitters, inconsistent time base information or network wide errors that may affect a plurality of channels.
Therefore, a need exists in the art for a method and apparatus for performing real time packet analysis without the associated high computational expense. Specifically, a need exists for a method and apparatus for detecting errors, verifying the consistencies of time base information and displaying important packet stream information.